Recent years have seen an increased interest in so called heat batteries for vehicular use. Such heat batteries typically include a heat storage medium which usually, but not always, is a phase change material such as a salt or a high specific heat single phase material. The battery includes an internal heat exchanger through which engine coolant is circulated. To charge the battery with heat, hot engine coolant that is heated during engine operation is passed through the heat exchanger and its heat rejected to the heat storage medium. Subsequently, the heat may be utilized to heat the passenger compartment or to immediately provide warm coolant to the engine for the purpose of reducing emissions and easing start-up wear by circulating now cold coolant through the heat exchanger to be warmed first and then passed to the engine. The stored heat may also be used to operate the vehicle defroster for immediate defrosting. At this time, heat will be rejected by the heat storage medium to the coolant to warm the same; and will thereafter be rejected to the engine to warm it.
In cold climates, the use of such heat batteries in vehicles is particularly desirable because they provide a means whereby hot coolant for use in a vehicle heater is immediately available upon entry into the vehicle and/or is available to warm the engine long prior to the time at which the engine would warm as a result of internal combustion occurring therein. The benefits of immediately being able to warm the passenger compartment are obvious. Those skilled in the art will also recognize that internal combustion engines produce the greatest quantity of undesirable emissions during start up. Cold or cool engines do not promote effective combustion of fuel and as a consequence, hydrocarbon emissions from uncombusted fuel may be substantial.
Prior attempts to provide commercially viable heat batteries have not proved all together successful. In one such attempt, the heat storage medium was a salt that could change between the solid and liquid phases in the temperature range of operation to absorb or reject the latent heat of fusion of the salt to maximize heat storage capability. Unfortunately, the material employed was highly corrosive which led to a number of obvious difficulties.
More recently, it has been proposed to utilize magnesium nitrate hexahydrate containing a small amount of lithium nitrate. This material works well but when placed in a heat battery formed of aluminum, gases are generated which must be vented.
It has therefore been proposed in European patent application EPO 770,844, the entire disclosure of which is herein incorporated by reference, to provide a means of venting the chamber of the heat battery containing the heat storage medium to avoid pressure build up. It is therein proposed to utilize a check valve that is soldered or otherwise located in an opening in the jacket defining the so called salt chamber (the chamber that contains the heat exchanger and the heat storage medium) which may then be connected to a vent opening to the coolant circulation system. While this approach has generally avoided the problem caused by pressure build up, it has not been 100% successful in so doing.
In particular, when a heat battery is mounted in a vehicle, it is subjected to all the forces that are encountered when the vehicle accelerates, decelerates, goes around a corner or skids on a skid pad resulting in substantial centrifugal forces, as well as the force of gravity as the vehicle travels over uneven or nonlevel terrain. In such situations, the heat storage material, if it is a phase change material, is most always in the liquid phase as a result of being heated by operation of the vehicle engine. The heat storage material, being in the liquid phase, may splash around within the salt jacket and onto the valve inlet. In some instances, it is conceivable that it could even immerse the valve inlet. If the salt is permitted to form a meniscus on the valve inlet, when the battery vents, the salt may enter the valve.
Entry of the heat storage material or salt into the check valve has been known to disable the check valve either resulting in its inability to open to relieve excess pressure or, more likely, in being unable to close, which may allow the interior of the salt jacket to freely vent to and from the cooling system, an occurrence that is undesirable.
The present invention is directed to overcoming one or more of the above problems.